Williams’s book and the BBC report describes some of the evidence that have surfaced in recent years that have cast doubt around the official explanation of how Hammarskjold’s plane crashed. Raising doubts is the way the crash scene was handled, a mysterious hole in Hammarskjold’s head that had been airbrushed from official photographs, and another plane which was spotted around Hammarskjold’s DC-6.

Who would want Hammarskjold dead?

Hammarskjold was en route to Congo, which in 1961 was embroiled in the complex politics of decolonization and cold war rivalry. Specifically, Hammarskjold was going to meet with Moise Tshombe, leader of the secessionist movement in the hopes of negotiating a settlement with the Soviet-backed, elected government of Congo. However there were other interested parties in the Congo most notably Belgium, the United States, and the United Kingdom, who had mining interests, and the White-led governments of South Africa and Rhodesia who feared the rise of African nationalism. Williams argues that these parties had “a sense of being at war with the UN and with African nationalism” and did not want Hammarskjold and Tshombe to reach a settlement.

As the BBC mentions in their report, Susan Williams emphasizes three discoveries that point to a cover-up:

*The photographs of Hammarskjold after his death are either taken in such a way as to conceal the area around his right eye, or, where the eye is visible, they show evidence of having been touched up, possibly to hide a wound

* The sole survivor of the crash, Harold Julien, said there was an explosion before the plane fell from the sky – his evidence was discounted in the original inquiry on the grounds that he was ill and sedated, but Ms Williams has found a doctor’s statement insisting that he was lucid at the time (he died of his injuries within days)

* A US intelligence officer at a listening station in Cyprus says he heard a cockpit recording from Ndola, in which a pilot talks of closing in on the DC6 – guns are heard firing, and then the words “I’ve hit it”

“There is no smoking gun, but there is a mass of evidence that points in the direction that the plane was shot down by a second plane,” she told the BBC. “That is a far more convincing and supported explanation than any other.”